This invention relates to a cable lug for mounting on the end of a cable for making electrical connection between a conductor of the cable and other electrical equipment.
Such cable lugs are well known for terminating electrical power cables, and comprise a palm for connecting the lug to the electrical equipment, usually by means of a bolt passing therethrough, and a barrel, integral with the palm and usually extending therefrom, for receiving the bared end of the conductor therein. The conductor may be retained in the lug barrel by crimping, or alternatively by means of securing bolts, which may be shear head bolts. The conductor may be solid or stranded, and will usually be of aluminium or copper.
The electrical equipment may be a transformer or switchgear, with the cable lug being connected to a bushing thereof, which may be by means of a cable adapter (T- or L-shape), such as sold by Tyco Electronics Raychem GmbH under the tradename RSTI for example. Insulation of the electrical connection may alternatively be effected by a heat-recoverable sleeve, also available from Tyco Electronics Raychem GmbH.
Such cable lugs are supplied for use with cables of a defined range of sizes, effectively diameters, and it is important to select the correct size lug for the cable. This leads to the need for holding a relatively large inventory, and its associated expense. Conventional cable lugs using bolt securement have an eccentric barrel, with the wall thickness on one side being greater then on the other side in order to provide sufficient length for the threads of the bolts to be gripped therein. This results in the cable being mounted eccentrically with respect to the lug, which can be disadvantageous when providing electrical insulation therearound. The thinner wall section, usually diametrically opposed, allows the weight and cost of the lug to be minimised. It is an object of the present invention to provide a cable lug that overcomes, or at least alleviates, problems of the known lugs.
Thus in accordance with one aspect of the present invention, there is provided a cable lug for mounting on the end of a cable for making electrical connection between a conductor of the cable and other electrical equipment, wherein the lug comprises a palm for connecting the lug to the electrical equipment, a generally elongate cylindrical barrel for receiving therein one end of the cable conductor, an insert for disposal within the barrel and for extending around and along the inner surface of the barrel, whereby in operation the insert is arranged to lie between the cable conductor and the inner surface of the lug, and means for retaining the insert against movement within the barrel.
The lug of the invention thus has a separate insert, and this allows a single barrel to be used with a much larger range of cable sizes, the insert being required and inserted for use with smaller cables. This can enable the barrel to be aligned more nearly concentrically on the cable end over the whole range of sizes, than would be possible with previously known lugs. The barrel wall can be, and preferably is, of substantially uniform thickness, which may be more economical to manufacture than known lugs of varying wall thickness. Further, the retention of the insert ensures good electromechanical securement of the cable conductor in the barrel of the lug. It is envisaged that the insert will extend only partially around the inner surface of the barrel of the lug, and may extend only partially or substantially the whole length of the lug barrel.
Advantageously, the insert will be shaped as part of a generally cylindrical surface, for conformity with the inner surface of the barrel of the lug. In this case, the insert will be circumferentially located within the barrel generally opposite the threaded aperture in the barrel by which the lug is secured to the cable. However, it is also envisaged that the insert may be of full cylindrical configuration, formed for example as a single pressing, in which case it is preferably apertured at diametrically-opposed locations to receive therethrough the means to secure the insert to the barrel and the means to secure the lug to the cable respectively.
It will be appreciated that retention of the insert is required during insertion of the cable conductor into the barrel in order to ensure good mechanical and electrical connection, and also advantageously prior to such insertion. The retaining means may secure the insert against rotational and/or longitudinal movement in one or both directions. The retaining means preferably comprises a projection of one of the barrel and insert, advantageously, of the insert, and a co-operating aperture of the other. Such interengagement may be provided at any suitable location along and around the insert. The aperture may be an indentation or a through-hole. It will be appreciated that two, or more, projections and respective apertures may be provided. In a preferred embodiment, the retaining means includes a hole extending completely through the side wall of the barrel.
Preferably, the cable lug is made of aluminium or copper. Consequently, it is desirable to tin the inner surface of the barrel of the lug, and the hole therein conveniently allows passivating solution to flow into, through, and out of the barrel. Advantageously, the insert and/or the barrel is grooved on its inner surface to enhance connection with the cable conductor. Such grooves may extend longitudinally or circumferentially. Advantageously, the grooves of the barrel are located only over its innermost region, beyond the position at which the lug is fixed to the cable. Preferably, at least one shear head bolt is provided for securing the lug to the cable. The cable lug of the invention may be sized to suit various cable sizes, for example diameters of 95 to 240 mm2 or 25 to 95 mm2.
It is understood that although the cable lug of the present invention is primarily for use with the termination of a cable, the other electrical equipment may itself comprise another cable. Accordingly, the cable lug may be employed in a cable joint, formed, for example, by the use of two such lugs fitted to respective cables.